Common Emitter Amplifier Circuit Working and Its Characteristics

There are different types of transistor amplifiers operated by using an AC signal input. Which are interchanged between the positive value and negative value, hence this is the one way of presenting the common emitter amplifier circuit to function between two peak values. This process is known as the biasing amplifier and it is an important amplifier design to establish the exact operating point of a transistor amplifier which is ready to receive the signals hence it can reduce any distortion to the output signal.

What is a Common Emitter Amplifier?

The common emitter amplifier is a three basic single stage bipolar junction transistor and is used as a voltage amplifier. The input of this amplifier is taken from the base terminal, the output is collected from the collector terminal and the emitter terminal is common for both the terminals. The basic symbol of the common emitter amplifier is shown below.

 Common Emitter Amplifier
Common Emitter Amplifier

Working of Common Emitter Amplifier

The below circuit diagram shows the working of the common emitter amplifier circuit and it consists of voltage divider biasing, used to supply the base bias voltage as per the necessity. The voltage divider biasing has a potential divider with two resistors are connected in a way that the midpoint is used for supplying base bias voltage.

Common Emitter Amplifier Circuit
Common Emitter Amplifier Circuit

There are different types of electronic components in the common emitter amplifier which are R1 resistor is used for the forward bias, the R2 resistor is used for the development of bias, the RL resistor is used at the output it is called as the load resistance. The RE resistor is used for the thermal stability. The C1 capacitor is used to separate the AC signals from the DC biasing voltage and the capacitor is known as the coupling capacitor.

The figure shows that the bias vs gain common emitter amplifier transistor characteristics, if the R2 resistor increases then there is an increase in the forward bias and R1 & bias are inversely proportional to each other. The alternating current is applied to the base of the transistor of the common emitter amplifier circuit then there is a flow of small base current. Hence there is a large amount of current flow through the collector with the help of the RC resistance. The voltage near the resistance RC will change because the value is very high and the values are from the 4 to 10kohm. Hence there is a huge amount of current present in the collector circuit which amplified from the weak signal, therefore common emitter transistor work as an amplifier circuit.

Voltage Gain of Common Emitter Amplifier

The current gain of common emitter amplifier is defined as the ratio of change in collector current to the change in base current. The voltage gain is defined as the product of the current gain and the ratio of the output resistance of the collector to the input resistance of the base circuits. The following equations show the mathematical expression of the voltage gain and the current gain.

Voltage & Current Gain of Common Emitter Amplifier
Voltage & Current Gain of Common Emitter Amplifier

Common Emitter Transistor Amplifier

The following circuit diagram shows the common emitter transistor amplifier. This transistor amplifier has a common configuration and it is a standard format of transistor circuit whereas voltage gain is desired. The common emitter amplifier is also converted as an inverting amplifier. The different types of configurations in transistor amplifiers are common base and the common collector transistor and the figure are shown in the following circuits.

Common Emitter Transistor Amplifier
Common Emitter Transistor Amplifier

Characteristics of Common Emitter Amplifier

  • The voltage gain of common emitter amplifier is medium
  • The power gain is high in the common emitter amplifier
  • There is a phase relationship of 180 degrees in input and output
  • In the common emitter amplifier, the input and output resistors are medium.

The characteristics graph between the bias and the gain is shown below.

Characteristics Graph
Characteristics Graph

Applications of Common Emitter Amplifier

  • The common emitter amplifiers are used in the low-frequency voltage amplifiers.
  • These amplifiers are used typically in the RF circuits.
  • In general, the amplifiers are used in the Low noise amplifiers

Advantages of Common Emitter Amplifier

  • The common emitter amplifier has a low input impedance and it is an inverting amplifier
  • The output impedance of this amplifier is high
  • This amplifier has highest power gain when combined with medium voltage and current gain
  • The current gain of the common emitter amplifier is high

Disadvantages of Common Emitter Amplifier

  • In the high frequencies, the common emitter amplifier does not respond
  • The voltage gain of this amplifier is unstable
  • The output resistance is very high in these amplifiers
  • In these amplifiers, there is a high thermal instability
  • High output resistance

This article discusses the working of the common emitter amplifier circuit. By reading the above information you have got an idea about this concept. Furthermore, any  queries regarding this or if you want to implement electrical projects, please feel free to comment in the below section. Here is the question for you, what is the function of the common emitter amplifier?

6 Comments

  1. very good & useful information for working of common emitter. I read this article

    1. Tarun Agarwal says:

      Hi Vivek
      Thank you for giving us a perfect rating

  2. Hy Tarun, nice article. I thoroughly enjoyed the way you delivered it. I am trying to design a voltage divider. What I want is, to check the impact of loading on the divider for common emitter amplifier. The calculator which I am using is at Now for checking the loaded output voltage and the current flowing towards the load I need to enter load RL. What should I do in the case of the common emitter? I actually want to ask the resistance of this amp,

  3. how phase inversion occur

    1. Tarun Agarwal says:

      Hi saqib
      I sincerely appreciate your kind response regarding my article.

      For the common emitter amplifier circuit, the input is applied to the base, and the output is taken from the collector. The common terminal for both circuits is the emitter. The common emitter transistor amplifier is the only configuration that gives an inversion, 180°, between the input and output signals.
      The reason for this can be seen from the fact that as the input voltage rises, so the current increases through the base circuit. In turn this increases the current thought the collector circuit, i.e. it tends to turn the transistor on. This results in the voltage between the collector and emitter terminals falling.
      In this way an increase in voltage between the base and emitter has resulted in a fall in voltage between the collector and emitter terminals, in other words the phase of the two signals has been inverted.
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